Direct injection gasoline engines offer improved efficiency because fuel injected directly into a cylinder can reduce cylinder charge temperature. As a result, additional air may enter a cylinder as compared to an equivalent cylinder that has port injected fuel. Consequently, engine power and efficiency may be improved. In addition, direct injection gasoline engines may exhibit improved transient fuel control because there is less tendency for fuel to collect at a cylinder intake port of a direct injection engine than for a port fuel injection engine. However, direct injection engines may generate soot at higher engine speed and load conditions because there is less time available to atomize fuel in the cylinder. As a result, it may be useful to incorporate a particulate filter in the exhaust system of a direct injection engine. Gasoline engines include those engines fueled by pure gasoline or mixtures of gasoline and other fuels such as alcohols. Further, other fuels used in spark ignited engines are also included such as liquid propane gas (LPG) or compressed natural gas (CNG).
In U.S. Pat. No. 6,738,702 a method for regenerating a particulate filter is described. In particular the reference describes a diesel engine having a particulate filter followed by a lean NOX catalyst or a SCR catalyst. The method describes adjusting engine fuel to provide an air-fuel ratio for purging catalyst. However, the method provides little detail as to how engine fuel is adjusted and any such adjustment is less likely to be effective for gasoline engines because gasoline engines are often operated at stoichiometric conditions whereas diesel engines are often operated with lean air-fuel mixtures.
The inventors herein have developed a method for adjusting fuel supplied to a spark ignited engine, comprising: adjusting an amount of fuel supplied to at least one cylinder of an engine in response to soot oxidized in a particulate filter; and spark igniting at least some of the amount of fuel in said at least one cylinder.
By adjusting fuel supplied to an engine in response to soot oxidized in a particulate filter and spark igniting a least a portion of the fuel delivered to the engine, engine exhaust gases can be controlled so that efficiency of a catalyst improves. In one embodiment, an oxygen sensor can be placed in an exhaust system at a location downstream of a particulate filter so that engine fuel can be adjusted as the rate of oxidation of soot held by a particulate filter varies. In this way, fuel delivered to an engine can be adjusted so that exhaust gases entering a catalyst are near a stoichiometric mixture. As a result, the catalyst conversion efficiency may be improved over engines that are simply operated with lean air-fuel mixtures during particulate filter regeneration.
The present description may provide several advantages. In particular, the description provides a method improving engine air fuel control since the amount of excess exhaust gas oxygen consumed during particulate filter regeneration can be accounted for in engine fuel delivery. Further, catalyst efficiency during particulate filter regeneration may be improved because engine exhaust gases can be controlled such that a catalyst is exposed to substantially stoichiometric exhaust gases. Further still, in some embodiments, exhaust gas excess oxygen consumed by oxidation of soot in a particulate filter may be accounted for without additional calculations by an engine controller.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.